Knowledge regarding the occupancy of a particular region or space can be useful in a variety of applications. For instance, knowledge of occupancy within a building can be used to improve the energy efficiency by the automation of lightning and heating, ventilation and/or air conditioning (HVAC), and can be used in emergency situations to improve search and rescue efforts of first responders by providing information regarding the location of occupants.
Passive infrared (PIR) motion sensors are often used for occupancy sensing. For example, PIR sensors are often used in combination with wall switches to turn on the lights in a room when a person enters, and turn the lights off at a fixed preset time duration after motion in the room is no longer detected. This type of system, however, can result in the lights in a room automatically turning off after a predetermined period of time after motion is last sensed, even if one or more people are still in the room.